Destructive thyroiditis presenting as thyrotoxicosis followed by hypothyroidism during lenvatinib therapy for hepatocellular carcinoma

Hypothyroidism is a common adverse event of lenvatinib therapy for hepatocellular carcinoma (HCC), whereas thyrotoxicosis has rarely been reported in clinical trials. A 74-year-old man complaining of abdominal pain was found to have liver tumors and paraaortic lymphadenopathy. The intrahepatic lesions were diagnosed as HCC by angiography and treated with transcatheter arterial chemoembolization. Although localized prostate cancer was discovered incidentally, the etiology of paraaortic lymphadenopathy was assumed to be metastatic HCC. Lenvatinib 12 mg/day was started when his thyroid function tests were almost normal but was interrupted because of thyrotoxicosis. The patient was negative for tested thyroid autoantibodies. Color Doppler ultrasonography detected reduced thyroid blood flow, suggesting destructive thyroiditis. Although he resumed lenvatinib at 8 mg/day once his serum level of free thyroxine normalized, thyrotoxicosis recurred. Subsequently, he suffered hypothyroidism, which exacerbated despite levothyroxine replacement. Lenvatinib was discontinued as it was ineffective against the paraaortic lymph node metastasis, and external-beam radiotherapy was performed. After the completion of radiotherapy, the thyroid dysfunction significantly improved. In summary, lenvatinib for HCC can induce transient thyrotoxicosis followed by hypothyroidism, which is compatible with destructive thyroiditis. During lenvatinib therapy, close monitoring of thyroid function and appropriate management of thyrotoxicosis as well as hypothyroidism are essential.